1. Field of the Invention
In general, the present invention relates to systems and circuits that are used to recharge batteries. More particularly, the present invention relates to systems and circuits that recharge large capacity batteries from an available AC power source.
2. Prior Art Description
Batteries store electricity and provide that electricity as a direct current when used. If a battery is designed to be recharged, that battery can only be recharged by receiving a direct current from an outside power source. Alternating current power sources cannot be directly used to recharge the battery. The use of an alternating current can damage or destroy a rechargeable battery. Furthermore, the DC voltage provided to a battery when recharging must be greater than the voltage rating of the battery. As such, it takes more than 12 volts to recharge a 12 volt battery. However, for many reasons inherent in the construction of a battery, a battery is best recharged by a voltage that is not much higher than the voltage rating of the battery. Thus, it is far better to recharge a 12 volt battery with a voltage of under 20 volts than it would be to recharge the same battery with a 120 DC volt source.
Most people obtain power from an electrical utility company through the use of the power grid that is provided by the company. In the United States, the power grid usually provides 240 volts and 120 volts at 60 Hz. Within a home or building, only one phase of power is used in most circuits. As such, most power outlets provide 120 volts at 60 Hz. In order to recharge a battery using a typical outlet, a battery charger must be used. The battery charger typically contains a transformer that lowers the output voltage to an acceptable range. The reduced output voltage is then rectified to convert the alternating current into a direct current. Lastly, a series of resistive elements are used to limit or fix the magnitude of the charging current. Without the use of the resistive elements, large rechargeable batteries would draw large currents and would blow fuses or trip circuit breakers in the home.
It will be understood that transformers and resistive elements create operating losses in power. According to Ohm's law, the power loss in Watts is equal to the resistance in Ohms times the current in amps, squared. Thus, if a battery charger for a large rechargeable battery has three Ohms of resistance, 2700 Watts of power are lost as the battery recharges.
The prior art is replete with rechargeable batteries and chargers for such batteries. Chargers for large capacity rechargeable batteries utilize both transformers and resistive elements. Thus, such prior art battery chargers inherently consume significant amounts of power as they operate, as has been explained. Such prior art battery chargers are exemplified by U.S. Pat. No. 4,333,134 to Gurwicz, and U.S. Patent Application Publication No. 2013/0026975 to Liu.
Many popular devices, such as phones and computers, use rechargeable batteries. However, such devices are relatively low power and contain small batteries that can be rapidly recharged using conventional methods. Due to the small size and power of the batteries, the inefficiencies inherent in the recharging systems for the batteries can be overlooked as being insignificant. However, in devices that use large rechargeable batteries, inefficiencies in prior art recharging systems become problematic, resulting in recharging systems that are both costly to operate and time consuming to use.
Consumer products, such as electric vehicles, with large powerful rechargeable batteries, are becoming more popular in the marketplace. In operation, many electric vehicles, such as electric cars, electric forklifts, and the like, can consume over one hundred kilowatts of power. Two of the largest factors that have hampered the consumer acceptance of such electric vehicles are the time and cost required to recharge the vehicle's large batteries. For example, there are electric vehicles being sold to the public that operate at 120 volts DC and use over 100 Kilowatts of power. In order to recharge such large capacity batteries from a traditional AC receptacle requires a large transformer to control voltage and numerous resistive elements to pace the large currents that can be drawn by such batteries. Using traditional recharging technologies, the power losses can easily exceed 1000 Watts. As such, the power lost by the prior art recharging system is large enough to run a household air conditioning system. Losses in power result directly in increased costs for the power drawn from the utility company.
A need therefore exists for an improved system and circuit that can be used to more efficiently recharge large capacity batteries from a household AC power source, wherein the system charges large batteries faster and wastes less power than traditional prior art charging systems. These needs are met by the present invention as described and claimed below.